The present invention is a log feeding device having a feeding wheel for feeding and guiding elongate objects having a substantially round cross section such as tree trunks, logs and similar objects. The object is fed relative to a wheel by bearing against a friction surface formed by the circumference of the wheel that is concentric with the longitudinal axis of the wheel. The friction surface may be described as a net of chain cables having chain strings that are connected to each other at intersections. The chain strings are, at each end, connected to an outer circumference of two side pieces attached to each wheel. The side pieces are concentric with the longitudinal axis of the wheel but are axially separated from each other. The chain cable net is supported by an elastic support surface that coincides with the friction surface. The support surface includes a peripheral surface of an elastic tire mounted to each of the feeding wheels.
The feeding wheel is used in machinery such as automated logging devices for harvesting timber. In this type of machinery, the feeding force is transferred to the tree trunk by two oppositely mounted feeding wheels each having a substantially vertical longitudinal axis. The trunk or log is guided so that the upper side of the trunk is horizontally fed through at a constant height relative to a device for removing branches from the trunk. The branch removing device is mounted subsequent to the feeding wheels. The bottom portion of the trunk is captured between the feeding wheels and the trunk is fed into the subsequently positioned branch removing device. The diameter of the trunk is often thicker at the bottom portion or root portion of the trunk and is gradually reduced toward the top portion of the trunk so that the diameter of the trunk is gradually reduced as the trunk passes between the feeding wheels with the root portion being fed in between the wheels first. The difference between the diameter of the bottom portion and top portion of a trunk may be substantial. When a forest is ready for thinning, the bottom portions of the tree trunks may have a diameter of about 35 centimeters and the top portion may have a diameter of about 5 centimeters or less. When the trees are ready for the felling stage, the bottom portions may be about 60 centimeters or larger and 5 centimeters or less at the top portion. The feeding wheels must therefore produce sufficient friction forces against the trunks during the whole process the trunks are being fed or guided therethrough despite the varying diameters of the trunks.
Accordingly, the trunk or log is horizontally fed with its upper side at a substantially constant height so that the upper side of the trunk is positioned at about the same level as the upper side of the feeding wheels and the upper edge of the elastic support surface. This means that the longitudinal axis of the trunk will also move vertically relative to the feeding wheels as the trunk is horizontally passed between the feeding wheels because the diameter of the trunk is becoming smaller and the trunk is pressed against an upper horizontal plate attached to the log feeding device. A trunk having a bottom portion with a diameter greater than the width of the feeding wheels is, at the beginning of the feeding process, positioned in an eccentric vertical position so that the under-side of the trunk is positioned below the under-side of the feeding wheels. As the trunk is fed through, the longitudinal axis of the trunk is positioned between the feeding wheels in a vertically centered position to finally be positioned in an eccentric vertical position so the under-side of the trunk is positioned above the under-side of the feeding wheels when the upper portion of the trunk, having a relatively small diameter, is passed between the feeding wheels.
The forces that affect the feeding process are mostly the rolling resistance of the feeding wheels, i.e. the deformation forces of the elastic tire that forms the elastic support surface, the branch removal forces and the friction forces formed between the branch removing knives and the trunk, and the friction forces formed between the ground and the tree crown being dragged thereon. The rolling resistance of the feeding wheels is of particular interest. It is desirable to achieve sufficient feeding forces at a specific feeding pressure, formed between the trunk and the feeding wheels, that, at the same time, is as low as possible to prevent damage to the surface of the trunk or log. In other words, the contact surface between the trunk and the feeding wheels should be as great as possible. This means that the feeding wheels having the net of chain cables mounted thereon must be able to effectively adjust themselves or conform to the shape of the trunk during the whole feeding process from the bottom portion of the trunk, having the greatest diameter, to the top portion having the smallest diameter. The net of chain cables must during this whole process conform to the trunk to effectively hold the trunk.
A known feeding wheel for holding and guiding tree trunks, according to Swedish patent SE 8902493-9, has two round side pieces and a net of cable chains including chain links that are connected to one another at points of intersections. This cable chain net has a concave profile and follows the shape of the concave rotation surface about the longitudinal axis of the wheel. The side pieces are preferably made of stiff metal plates and the points of attachment along the periphery of the plates can be somewhat compliant in the direction of the longitudinal axis. This construction is an improvement compared to the earlier known feeding wheels for this particular purpose. However, the construction has some limitations when it comes to effectively adjust itself, during the feeding process of the trunk, to the varied diameter of the trunk from the bottom portion to the top portion of the trunk. The concave profile of the wheel provides a relatively large contact surface between the trunk and the wheels which is advantageous. However, this concave profile may also provide a drawback when the top portion of the trunk is passed through the wheels. Since the feeding wheels have a relatively small diameter but a large width, the smallest possible concavity may be too large so that the peripheral surfaces of the wheels touch each other which reduces the pressure exerted against the trunk placed and guided between the wheels.
Another known feeding wheel for the intended purpose, according to Swedish patent SE-9000590-1, also uses a concentric friction surface having the form of a net of cable chains that conforms to a rotation surface having a concave symmetrical profile relative the longitudinal axis of the wheel. The net of cable chains is supported by or bears against, in this case, an elastic support surface that coincides with the rotation surface. The support surface includes a peripheral surface of an elastic tire mounted on the feeding wheel. The net of cable chains is connected to the rim of the feeding wheel and extends across the edge portions of the elastic support surface. In this case, the ability of the concave net of cable chains to evenly grip is combined with elasticity and the adaption characteristics of a rubber wheel. The risk of slippage between the wheel rim and the net of chain cables, attached to the rubber tire where the net of chain cables is not in contact with the wheel rim, is eliminated. The rubber tire may be a pneumatic tire or a solid rubber tire vulcanized to the wheel rim. During the feeding process, the rubber tire is subjected to substantial deformation followed by considerable heating of the tire and fatigue of the rubber material. This is particularly evident when the rubber tire is exposed to a tree trunk, during the feeding process, that has a successively varied diameter because the rubber tire is subjected to unevenly distributed deformation. The deformation of the rubber tire changes as the diameter of the tree trunk changes and the rubber material is fatigued. Pneumatic tires are therefore often punctured and solid tires have a tendency to detach from the tire rim.
An object of the present invention is to develop a feeding wheel that combines the constructive stability of the feeding wheel with a friction surface that includes a cable chain net that is attached to the outer periphery of side plates attached to the feeding wheel. The net has the ability to conform to the shape of the feeding wheel so that the net is supported by an elastic support surface that easily conforms to the shape of a tree trunk to effectively hold and guide the tree trunk as the diameter of the tree trunk is being reduced from its thick root portion to the thin top portion. Due to the improved ability to grip or hold the tree trunk, less pressure forces on the tree trunk and less driving forces of the feeding wheels are required.
The elastic tire has an outer profile, including the cable chain net attached thereto, that may extend along a straight line that is parallel to the longitudinal axis of the feeding wheel or the outer profile may be curved compared to the longitudinal axis of the wheel when viewed in a cross-sectional view through the longitudinal axis of the wheel.
When the cable chain net is provided in the form of a so called diagonal net, the chain strings extend between the connection points so that a first set of chain strings is sloping in a direction that is opposite to a second set of chain strings relative to the longitudinal axis of the wheels. The length of the chain strings, when stretched, is greater than the distance as represented by a straight line between the respective connection points. In this way, the chain strings, when not under load by the wheel, may be in an outwardly curved state. When the chain strings are under an inwardly directed radial load, the chain strings may, as the elastic tire is being deformed, first be in slack position and eventually be in an opposite inwardly curved and stretched position. In this position, the chain strings take tap a substantial amount of the load applied by a tree trunk that is positioned approximately right in between the side pieces of the feeding wheels.
The elastic tire may be made of a solid material. In the preferred embodiment, the tire has a chamber formed therein that is concentric with the longitudinal axis of the wheel. The chamber is open towards the rim of the wheel and is confined by the side portions of the elastic fire. The side portions have a relatively thick wall thickness compared to a midportion that has a relatively thin wall thickness.
The latter embodiment of the elastic tire permits a smooth adjustment to an object having a varied diameter such as root and top portions of a tree trunk, when there is a relatively large contact surface between the tree trunk and the elastic support surface of the feeding wheel.
The process of feeding an object, such as a tree trunk having a relatively thick root portion and a thinner top portion, may be described as follows.
During the feeding process, the upper side of a horizontal tree trunk bears against a stationary upper support plate that is at about the same height as the upper side portions of the feeding wheels. The tree trunk is fed therethrough with the root portion first. The root portion may have a diameter that is greater than the vertical distance between the side pieces of the feeding wheel. In the beginning of the feeding process, the tree trunks bears, via the cable chain net, against the respective lower portions of the elastic tires of the feeding wheels that are positioned on each side of the horizontal tree trunk. As mentioned earlier, the upper side of the tree trunk bears against the support plate. In this way, the elastic tires are subjected to inward elastic pressure. The cable chain net conforms to the deformation of the elastic tires at the contact areas of the peripheral portions of the feeding wheel. The elastic pressure against the tree trunk is essentially provided by the lower comer portion of the elastic tire. The tree trunk is guided in this way by three elements including the opposite feeding wheels and the upper support plate.
As the feeding process progresses, the diameter of the tree trunk is being reduced so that the tree trunk will eventually reach a position whereby its longitudinal axis is right between the side plates so that the tree trunk, via the cable chain net, exerts a pressure against a mid portion of each elastic tire. The mid portion of the elastic tire provides less deformation resistance compared to the comer portions so that the cable chain net takes up an increasing amount of pressure until the chain strings are stretched and net reaches a point of maximum inner deformation. The tree trunk is now substantially guided by the oppositely facing cable chain nets and the chain strings substantially enclose a portion of the tree trunk at opposite sides. The relatively thin mid portion of the elastic tire, as well as the comer portions of the tire, only provides minor pressure resistance in this situation.
As the feeding process progresses further, the relatively thin upper portion of the tree trunk bears, via the cable chain net, against both elastic tires and the upper stationary support plate. In this situation, the upper comer portion of the elastic tire is again subject to pressure forces from the tree trunk and the tree trunk is held by the stretched chain strings that follow and bear against the lower peripheral surfaces of the elastic tire.
The above described feeding process uses an elastic tire having a chamber defined therein and the tire has a mid portion with relatively thin wails. A similar process takes place when a solid elastic tire is used that is made of a material with suitable compression characteristics. This applies both to solid and hollow elastic tires having a straight profile or a suitable concave profile so that the radial outer periphery of the support surface is symmetrically curved relative to the longitudinal axis of the feeding wheel.
Because the feeding wheel is slidably mounted on the rim, and not attached thereto by a vulcanization process, it is no longer necessary that the rim is made of a material, such as steel, that is suitable for vulcanization of robber. The wheel rim may instead be of another lighter material such as a suitable light metal alloy. In this way, a feeding wheel having a light weight may be used which is particularly important for harvesting equipment of the one-grip type.
An embodiment of the present invention is described below with references to the attached drawings.